Can someone kindly tell me how to demagnetize a magnet?
It's an ordinary bar magnet as used in some cupboards to keep them closed. It's too powerful for my needs and I want to demagnetize it by about 50%.
Should I strap it to another magnet with th epoles oritented +to+ and
- to - ? Would that work, and if so, how long will it take?
Many thanks,
Al
No.
Try one or two layers of tape over the magnet face - the attraction decreases dramatically with distance.
Would'nt it be quicker to get another? or set the magnet slightly further back into the cupboard?
I don't think magnets work like that. You could move it slightly away from the metal plate it attracts and put something in between them. Like a piece of thin steel/iron/copper?
alex
Increase the "air" gap, stick some non magnetic material in the gap, such as plastic or copper or AL
Wave a much stronger magnet at it.
I made a notice board with the help of this group. Used sheet metal on the wall and industrial strength magnets. The magnets are tiny but boy are they powerful! They will fly to the sheet from 5cm away. They stick through
10-20 sheets of paper.Tip: this has made a super way of storing/filing crap but their shape is a problem. They are little discs and if the flat edge sticks to flat metal surface its hard to get them off. God forbid one meets another! never the twain shall part. Nasty nip if the finger gets in the way. Ball shaped would work better. But they are great entertainment.
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Permanent magnets can be demagnetized in the following ways: Heat. Heating a magnet past its Curie point will destroy the long range ordering. Contact. Stroking one magnet with another in random fashion will demagnetize the magnet being stroked, in some cases; some materials have a very high coercive field and cannot be demagnetized with other permanent magnets. Hammering and/or Jarring. Such activity will destroy the long range ordering within the magnet. Being placed in a solenoid which has an alternating current being passed through it. The alternating current will disrupt the long range ordering, in much the same way that direct current can cause ordering.
Or sticky foam pads.
DG
Thanks to everyone for the replies. Yes, inserting some copper or aluminium (or something else, non-ferric, that doesn't conduct magnetism) beween the magnet and the contact plate seems to be a good idea in this case. Thank you!
Al
You are looking for a degausser - which uses AC to create an alternating magnetic field which randomises the alignment of the magnetic dipoles (just had a schoolboy physics flashback!).
Similar items were used to degauss TV tubes and very much larger ones on naval minesweepers before they started building them out of plastic
But the best solution is to increase the airgap as others have suggested.
I had a similar problem and I solved it with a piece of sellotape!
A decent demagnetiser will cost a couple of hundred quid and it will remove all the magnetism, which rather defeats the object.
Colin Bignell
Degaussing / demagnetising would totally demagnetise it. There is no way to partially demagnetise something. Try partially hitting it with a hammer and you will see what I mean.
A soldering iron is good for degaussing TVs.
Go for the gap method. Stickypads (gappy and dampening) or loosen the screws and move the magnet back if it is mounted on slotty holes.
Bob
NO, but a Soldering Gun is, as it has a transformer inside to create a magnetic field.
Dave
I think that was the method that was lurking deep in the murky depths of my memory somewhere. However, I'm not clear how long it would take to sit thee waving the stronger magnet before any difference was made.
Since posting my question, someone else suggested "shunting" the magnet. Has anyone heard that term before? Apparently you can "shunt" a magnet using steel nails, somehow. Out of curiosity, can anyone clarify how?
Al
Either works - with the soldering iron, you just heat it above the curie point :)
Think of a horseshoe magnet as favoured in Road Runner and Bugs Bunny cartoons. Imaginary "Lines of force" go between the two poles. If a piece of soft iron, which is easily magnetised, is placed between the two poles the lines of force will travel through the piece of iron because it's "easier" than going through the air. Because there now are less lines of force going through the air (because a lot of them are going through the iron) the magnetic field near the poles of the magnet will be found to be weaker than it was.
If your magnet is a bar magnet or a disk magnet the same still applies only the geometry is different
DG
DG, Thank you for the explanation. Can you explain why they always used to recommend (re: horseshoe magnets) that one should leave a piece of steel accross the poles while it is not in use? I recall that, when I was a kid, those red-and-silver (always red & silver, for some reason) horseshoe magnets were invariably sold with a piece of steel placed accross the poles... Perhaps it was a misconception, and they thought it would preserve the magnetism rather than weaken it...
Al
You take the keeper off before using the magnet, if you're using it to weaken the magnetic field you leave it on.
I've used the detachable 12V transformer from my halogen desklamp to degauss an old monitor that had a car speaker land on it.
I file a fair bit of crap on window frames this way. The strongest magnets I have are voice coil magnets from an old hard disk. They're curved bar magnets, and the back is "shorted" with the block they're mounted on.
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